BI3452_24_25_PART_1
Page 24: Terminology
Transcranial Electrical Stimulation (tES)
Umbrella term for methods using current passing through the scalp into brain tissue.
Includes:
Transcranial Direct Current Stimulation (tDCS)
Transcranial Alternating Current Stimulation (tACS)
Transcranial Random Noise Stimulation (tRNS)
Future methods not yet defined.
Page 25: tES – The Modern Era
Reference: Nitsche and Paulus, 2000
Discussed excitability changes in human motor cortex due to weak tDCS.
Measurement of tES effects:
Using Transcranial Magnetic Stimulation (TMS) to produce Motor Evoked Potential (MEP) in peripheral muscle.
Effect size is assessed by comparing pre-tES MEP and post-tES MEP amplitudes.
Page 26: tDCS over M1 and Measurement Techniques
tDCS applied to M1 (primary motor cortex)
TMS is used to assess MEP changes.
EEG data collection aids in indexing cortical excitability.
Page 27: Equipment Check
TMS Setup:
Wire coil stimulation setup.
Pulsed magnetic field with a positioning frame.
Parameters to note:
Maximum field depth and stimulated brain region.
Recording background EMG from FDI muscle for MEP analysis.
Latency analysis through descending volleys and MEP amplitudes measured through resting neurons (1 mV peak).
Page 28: Effects of Scalp DC Stimulation
Conducted scalp DC stimulation for 5 minutes at 1 mA in 19 subjects:
Results indicated that after cathodal DC stimulation, the excitability decreased.
Conversely, anodal DC stimulation led to an increase in the size of the evoked response.
Reference: Nitsche & Paulus, 2000; analysis included control conditioned responses.
Page 29: Spatial Specificity of tDCS
Anodal/cathodal effects observed when targeting the motor cortex with contralateral forehead montage (A).
No significant effects found with varied electrode montages (B).
Reference: Nitsche & Paulus, 2000.
Page 30: The Neurochemistry of tDCS
Investigating ion channel activity influenced by tDCS application in neuronal activity and response modulation.
Page 31: Linking Ion Channel Activity to tDCS
Anodal stimulation leads to depolarization, while cathodal stimulation hyperpolarizes neurons (Purpura & McMurty, 1965).
Investigating mechanisms and their differences between stimulation phases.
Importance of targeting channels/receptors in short-term and long-term tDCS protocols (4s vs. 9-13min).
Page 32: tDCS On Drugs I
Agents utilized in studies:
CBZ (Carbamazepine): Na+ channel blocker
FLU (Flunarizine): Ca2+ channel blocker
DMO (Dextromethorphan): NMDA channel blocker
PLC (Placebo)
Reference: Nitsche et al., J Physiol, 2003.
Page 33: tDCS Over M1 and Measurement Techniques (Reiterated)
Similar methodology as previously described for assessing MEP sizes using EEG.
Page 34: tDCS On Drugs II
Short-term anodal tDCS effects negated by sodium channel blockers; they showed reduced effects with calcium channel blockers.
Cathodal tDCS effects remained unchanged.
Reference: Nitsche et al., J Physiol, 2003.
Page 35: tDCS On Drugs III
Study with CBZ demonstrated total abolition of prolonged excitability enhancement caused by anodal tDCS under PLC condition.
Reference: Nitsche et al., J Physiol, 2003.
Page 36: tDCS On Drugs IV
Ca2+ channel blocker effects only impacted anodal tDCS, while cathodal responses remained intact.
The NMDA antagonist DMO affected both anodal and cathodal tDCS after-effects.
Page 37: tDCS On Drugs - Summary
Short-lasting tDCS (4s):
Linked to membrane polarization changes
Anodal tDCS in animals causes neuronal depolarization, with effects unclear for cathodal stimulation.
Long-lasting tDCS (minutes):
Influenced by NMDA receptors, which are crucial for effects beyond rapid ionotropic changes.
Possible intracellular changes in Ca2+ levels implicated.
Page 38: McBreak Time!
A humorous intermission, no academic content relevant.
Page 39: tDCS Meets MRS I
Introduction to Magnetic Resonance Spectroscopy (MRS) for in-vivo metabolite measurement in the human brain.
The use of MR scanners to estimate neurotransmitter concentrations.
Reference: Stagg et al., 2009.
Page 40: tDCS Meets MRS II
Graphical data showing changes in metabolite levels (Glx, GABA, NAA) due to anodal and cathodal tDCS compared to sham conditions.
Study reference: Stagg CJ et al., J. Neurosci. 2009.
Page 41: tDCS Meets MRS III
Additional graphical data indicating % changes in inhibitory (GABA) and excitatory (Glx) neurotransmitter levels post-tDCS.
Page 42: Beyond 'Direct' Current Stimulation
Overview of additional methodologies succeeding direct stimulation in research.
Page 43: The Different “Flavours” of tES
Visual representation highlighting variations of tES:
tACS: Transcranial Alternating Current Stimulation
tDCS: Transcranial Direct Current Stimulation
Sham: Control stimulation types.
Page 44: tRNS – Transcranial Random Noise Stimulation
Defines the method: Uses random noise frequency pattern to desynchronize abnormal brain rhythms (0.1-640Hz) without true randomness.
Literature mentions: 10 mins of stimulation yielding effects lasting 60 mins on physiological measures and behaviors (Terney et al., 2008).
Page 45: Terney et al. Study on tRNS
Describes frequency distribution and analysis of stimulation output in research.
Page 46: tACS – Specifics
Focuses on modulation of cortical rhythms through discrete frequency application, suitable for EEG/MEG studies.
Page 47: tACS – Entrainment Challenges
Examines issues in MEG studies with stimulation waveforms correlated with brain rhythms, emphasizing the need to isolate intrinsic oscillations from stimulation artifacts.
Page 48: Experimental Design Overview
Details on the electrode montage, stimulation types, and design used in the study involving 16 participants across 4 MEG visits for comprehensive data collection.
Page 49: Experimental Design - Trial Timeline
Outlines timings in experimental trials concerning stimulus administrations and response measures.
Page 50: MEG/tDCS Integration Example
Illustrates various conditions regarding sham and anodal tDCS pre- and post-conditions analyzed in the study.